The present invention relates to implantable medical leads for connection between a stimulating control device and one or more stimulation or sensing electrodes and methods of manufacturing such leads, and more particularly to methods of manufacturing flexible and extensible implantable medical leads.
Systems and methods for electrical stimulation of electrically excitable tissue within the body of a living subject have been developed utilizing stimulating electrodes and a signal generator or control device to supply electrical charges in a controlled or predetermined manner. Such systems and methods have been developed specifically based upon a desired condition, such as to alleviate pain or to stimulate muscle movement, and based upon the application with a subject's body. For bodily applications where the alleviation of pain is the goal, one or more stimulating and/or sensing electrodes can be implanted within nerve tissue, the brain or spinal cord for blocking pain sensation by electrical stimulation. For muscle tissue stimulation, a stimulating electrode can be implanted in a muscle tissue, whereby electrical current that is typically provided as pulses can cause muscle tissue reaction that may be controlled to cause movement of a subject's body part. Sensing electrodes are used for determining actions of the body.
Signal generators can determine when, how long, and/or the amperage of current pulses that are to be applied for the specific application, and often include hard-wired circuitry, a microprocessor with software and/or embedded logic as the controlling system for determining and dictating current pulses. Such signal generators may also be implanted within the subject's body, and typically such an implantation is done to position the signal generator close to the stimulating and/or sensing electrodes, with interconnecting medical leads for conducting current pulses to and from the stimulating and sensing electrodes. Implantable medical leads and externally utilized leads for these purposes are typically insulated conductors or conductive elements (e.g., a conductor disposed within a lead body), with conductive terminations at both ends for electrical connection with the signal generator and one or more electrodes. Implantable medical leads further have requirements for safe interbody use such as tissue compatibility, surgical procedure dynamics, and body fluid accommodation.
Signal generation and muscle tissue stimulation systems have more recently been envisioned for more complex control of a subject's bodily actions. One particularly complex muscular control concept has recently been considered for the purpose of re-teaching a subject how to swallow, the condition of inability to swallow being known as dysphagia. Techniques and methods of stimulating muscles within the neck region of a patient for the purposes of causing specifically determined muscles to react as a swallowing effect are described in PCT Publication No. WO 2004/028433, having a publication date of Apr. 8, 2004. Specifically, by implanting electrodes in two or more muscles of the upper airway musculature and connecting the electrodes with a signal generator that provides coordinate control signals, a swallowing action can be induced in the patient. Other specific techniques and methods are also disclosed in U.S. Pat. Nos. 5,725,564; 5,891,185; 5,987,359; 6,104,958; and 6,198,970; all to Freed et al. Other techniques and methods are disclosed in U.S. patent application Ser. No. 11/611,365, filed Dec. 15, 2006, and entitled “Method and Apparatus for Assisting Deglutition.” The teachings of each of these references are incorporated herein by reference in their entireties.
For these and other implanted electrode stimulation treatments, conventional leads may not be optimal. For example, a lead implanted (e.g., tunneled) from the patient's chest (e.g., from a stimulation signal generator) to the neck (and thus within tissue of the neck) should allow for the patient's head and neck to perform natural movements (including gross movements such as turning, raising and lowering of the head, etc.), as well as fine movements such as those associated with swallowing. Other bodily regions present similar movement concerns or constraints. With this in mind, and as mentioned above, medical leads include a conductor or conductive element maintained by a lead body (e.g., an insulative covering) with conductive terminations at the ends thereof for electrical connection to other components of the treatment system, such as a signal generator, electrode(s) (e.g., a stimulation electrode, a sensing electrode, etc.) and/or a lead extension. To this end, conventional leads typically exhibit limited longitudinal extensibility (e.g., will not longitudinally “stretch”). As such, when implanted in bodily regions that are normally subjected to movement by the patient, such movements can impart a tension-type force onto the lead (e.g., a lead running from the chest to a muscle or other tissue in the patient's neck will be subjected to a tensioning force with movement (such as tilting) of the neck/head). Due to the limited extensibility of conventional leads, the lead cannot accommodate the desired movement, but instead may overtly resist the tension force. This resistance, in turn, limits the ability of the patient to physically perform the desired movement.
Providing extra length or “slack” in a lead's length as it is connected between a signal generator and an electrode could potentially accommodate physical movements. However, the flexibility of such a lead would initially and uncontrollably allow lead portions to sag or collect within bodily cavities, spaces between tissue layers, etc. Moreover, if lead slack were to gather in a bodily cavity and/or between tissue, lead extension may then be limited or uncomfortable as the lead may slide or be pulled through tissue layers, or from the bodily cavity, in connection with physical movement of the bodily region in question. Resultant discomfort and/or pain can have the effect of limiting the patient's normal movements to the same extent as described above, as the patient will consciously or sub-consciously decide not to perform uncomfortable movements. Also, after a lead is implanted for some time, the lead begins and gradually adheres to one or more of the adjacent tissue, particularly in area(s) of lead sag or collection of excess lead material. As a result, the extra length of any such lead would no longer be available to permit desired extension (in otherwise accommodating desired movement of the bodily region in question).
In light of the above, a need exists for a lead configuration exhibiting enhanced flexibility and extensibility, and methods of making such leads.